This invention relates in general to methods of joining materials such as polymers, and in particular to methods of joining polymers using ultrasonic energy.
Ultrasonic (high frequency vibratory) energy has been used in polymer forming processes in several different ways. One class of applications involves the use of fixed-frequency ultrasonic energy for enhanced mixing or densification. For example, a means to affect the size of crystalline phases in thermoplastic polymers using ultrasonic energy is described in U.S. Pat. Nos. 3,298,065 and 4,288,398. Ultrasonic energy has also been used in a process for making directionally-oriented thermoplastic polymer articles via melt-oscillation.
Another class of applications entails the use of variable-amplitude ultrasonic energy to affect polymer melt rheology. This is described, for example, in U.S. Pat. No. 5,885,495, in which ultrasonic energy is used to affect polymer melt viscosity prior to molding.
Ultrasonic energy has also been used to join two solid polymer parts by generating heat through friction at a desired interface, a process commonly known as ultrasonic welding. U.S. Pat. No. 5,830,300 is but one of many examples of ultrasonic welding. In a typical process, ultrasonic energy is transferred from an energy source to a metallic horn that focuses the energy in a desired manner. The horn is placed in contact with the polymer parts, and mechanical vibrations are transferred from the horn to the parts. The vibrations generate heat through friction at the interface between the solid parts, which is sufficient to melt the parts at the interface. When the parts cool and solidify, a bond is formed at the interface between the parts.
As described in U.K. Patent Application GB 2,306,378-A, ultrasonic energy has also been used in process of injection molding a polymer to make hubcaps. In the process, a molten polymer is injected from a nozzle and is separated into two flow fronts as it flows around an insert in the mold. The flow fronts converge on the other side of the insert. Ultrasonic vibrations are applied to the molten polymer to mitigate against the formation of weld lines in the molded hubcap at the location of the converging flow fronts.
There is no suggestion in the prior art of using ultrasonic energy to improve the bonding of a molten polymer to a previously formed solid polymer part. Also, there is no suggestion of using ultrasonic energy to improve the bonding of different types of molten polymers to each other, such as during a molding or extrusion process.
The present invention relates to a method of joining a solidifiable liquid polymeric material to a solid material to produce a solid article. In the method, the solid material is contacted with the liquid polymeric material at an interface. Ultrasonic energy is applied so that the energy reaches the interface between the contacting solid material and liquid polymeric material. A joint is formed at the interface by allowing or causing the liquid polymeric material to solidify, to produce a solid article comprising the solidified polymeric material joined to the solid material.
In another embodiment, the invention relates to a method of joining a first solidifiable liquid polymeric material to a second solidifiable liquid polymeric material to produce a solid article, where the first and second liquid polymeric materials are materials of differing composition. The method involves contacting the first liquid polymeric material with the second liquid polymeric material at an interface. Ultrasonic energy is applied so that the energy reaches the interface between the contacting first polymeric material and second polymeric material. A joint is formed at the interface by allowing or causing the first polymeric material and the second polymeric material to solidify, to produce a solid article comprising the solidified first polymeric material joined to the solidified second polymeric material.
In another embodiment, the invention relates to a method of joining a first material to a second material in a molding process to produce a solid article. The first material and the second material are materials of differing composition, and at least one of the first and second materials is a solidifiable liquid material. The method involves introducing the first material and the second material into a mold, thereby contacting the first material with the second material at an interface. Ultrasonic energy is applied so that the energy reaches the interface between the contacting first material and second material. A joint is formed at the interface by allowing or causing the liquid material to solidify, to produce a solid article comprising the solid first material joined to the solid second material.
In another embodiment, the invention relates to a method of joining a first solidifiable liquid material to a second solidifiable liquid material in an extrusion process to produce a solid article, where the first and second materials are materials of differing composition. The method involves extruding the first material and the second material, thereby contacting the first material with the second material at an interface. Ultrasonic energy is applied so that the energy reaches the interface between the contacting first material and second material. A joint is formed at the interface by allowing or causing the first material and the second material to solidify, to produce a solid article comprising the solid first material joined to the solid second material.
In another embodiment, the invention relates to a method of joining a solidifiable liquid polymeric material to a reinforcement material or a filler. The method involves contacting the reinforcement material or the filler with the liquid polymeric material at an interface. Ultrasonic energy is applied so that the energy reaches the interface. A joint is formed at the interface by allowing or causing the polymer to solidify, to produce a material comprising the solidified polymeric material joined to the reinforcement material or the filler.
In a further embodiment, the invention relates to a method of joining a first material to a second material to produce a solid article, where at least one of the first and second materials is a solidifiable liquid material. A solid or liquid compatibilizing material is provided along with the first and second materials. The first material and the second material are contacted with the compatibilizing material, to form at least one interface between at least two of the compatibilizing material, the first material and the second material. Ultrasonic energy is applied so that the energy reaches the at least one interface. At least one joints is formed at the at least one interface by allowing or causing the first material and/or the second material to solidify in contact with the solid compatibilizing material, or by allowing or causing the first and/or second materials and the liquid compatibilizing material to solidify. A solid article is produced comprising the first material, the second material and the compatibilizing material joined together. The application of the ultrasonic energy improves the integrity of the joint(s) compared to the same method without the application of ultrasonic energy.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.